1. Field of the Invention
The present invention relates to an induction device, particularly to a high-efficiency induction device.
2. Description of the Prior Art
It is well known that an inductor may be applied to form a low-pass filter, and that the efficiency of the low-pass filter may be further improved by means of increasing the insertion loss resulting from the application of an additional capacitor.
In traditional technology, the combination of inductors and capacitors are realized by serially connecting one terminal of a substantial capacitor, i.e. a ceramic capacitor, to two inductors, thereby forming a three-terminal low-pass filter. As shown in FIG. 1(a), a traditional low-pass filter is comprised of a ceramic capacitor 10, two inductors 20, and three terminals 31, 32, 33. The two inductors are connected to one terminal of the ceramic capacitor 10, thereby forming the equivalent circuit shown in FIG. 1(b). This structure has the disadvantage of high cost and large volume and may not be fabricated to be a surface-mounted type (SMT) device.
Therefore, a SMT low-pass filter with low production cost is required in the industry.
The purpose of the present invention is to provide a filtering induction device.
The induction device provides an improved filter effect via the increase of an insertion loss resulting from stray capacitance. The induction device is comprised of a core structure, and first and second flat coils that interlacing with each other. The first flat coil is used as an inductor, and the second flat coil is used as an electrode board that belongs to a capacitor formed between the circles of the first flat coil.
The filtering induction device of the present invention is comprised of a core structure and two flat coils, a first flat coil and a second flat coil. The first flat coil is formed by winding a first conductive strip to form a spiral comprising at least one circle. The cross-section of the first conductive strip is a rectangle, and the first conductive strip is comprised of a first upper surface and a first lower surface. The circles each have the same first radius and are arranged layer by layer, wherein the first conductive strip is covered with an isolation material, such that the first flat coil is used as an inductor.
The structure of the second flat coil is similar to that of the first flat coil. The second flat coil is formed by winding a second conductive strip to form a spiral comprising at least one circle. The shape of the cross-section of the second conductive strip is a rectangle, and the second conductive strip is comprised of a second upper surface and a second lower surface. Particularly, the circles each have the same second radius and are arranged layer by layer, wherein the second conductive strip is covered with an isolation material or dielectric material. In this embodiment, the first and second radius may or may not equal.
According to theories about plate capacitors, because of the coverage of the isolation or dielectric material, the stray capacitance will be formed between the first upper surface and the first lower surface. Two capacitors can be formed by inserting an electrode board between these two surfaces. In this invention, the second flat coil is used to provide a plurality of equivalent electrode boards.
In the present invention, each circle of the second flat coil is inserted between opposite sections of the first upper surface and the first lower surface, such that the second upper surface is opposite to the first lower surface and the second lower surface is opposite to the first upper surface. In operation, the second flat coil is grounded with a terminal. Because the shapes of the first and second flat coils are both spirals, interlacing the two flat coils together would effectively compose a low-pass filter.
The coil assembly composed of the first and second flat coils is disposed in a core structure. The core structure, for example, is comprised of a core base and a core cover. By forming the core cover on the core base containing the coil assembly, the fabrication of the low-pass filter of the present invention is completed.